Bernie Sanders very nearly pulled off an upset in the Iowa caucuses on Monday night. Does this mean he will win the Democratic nomination? Probably not — Iowa is a very favorable state for him and he couldn't quite pull it off. But even if he isn't the nominee, the traction his campaign is getting is excellent news for progressives.

Hillary Clinton has certainly been getting the message. Her populist speeches, emphasizing taxing the wealthy to pay for spending on liberal programs like early childhood education and infrastructure, have definitely moved beyond the "era of big government is over" caution she and her husband have generally been associated with.

This is not to say, of course, that Clinton has fully adopted Sanders' policies and worldview — there remain real differences between them. In his post-caucus speech, Sanders emphasized some of the issues where he's to the left of Clinton, like a proposed $15 minimum wage and free tuition at public universities. But the differences between Sanders and the party establishment's preferred candidate are much less than they would have been 20 years ago.

Still, liberals have some reason for skepticism. Is Clinton just tacking left for the primaries in response to the success of the Sanders insurgency? Will she go back to her '90s self if she wins the nomination?

I don't think so. In part, Clinton may be reacting to Sanders. But really the power of Sanders' challenge is as much effect as cause. It represents a Democratic coalition that is well to the left of where it was in 1994 or 1976. The political landscape has changed, and even Bill Clinton would govern very differently if he took office today than he did in the '90s.

For example, Hillary Clinton has been forcefully arguing for an end to mass incarceration and denouncing the racist effects of these policies. But, as first lady, she supported the 1994 omnibus crime bill signed by her husband that severely exacerbated the problem. Some liberals are surely worried that the 1994 statute represents the "real" Clinton and she'll go back once the primaries are over.

I don't think, in this case, there's much basis for concern. It's important to understand the politics of the era, and how much things have changed. The 1994 omnibus crime bill had, at the time, broad support within the Democratic coalition. Only two Democratic senators voted against the bill, and one was the conservative Alabaman Richard Shelby. Among the members of the House who voted for the bill was…Bernie Sanders. The statute was, in retrospect, a terrible mistake, but it was based on bad assumptions that were widely shared by liberal and moderate Democrats alike at the time. Neither Clinton nor Sanders would make the same mistake again.

Or take gay and lesbian rights. Bill Clinton thought it was politically necessary to sign the appalling Defense of Marriage Act after it passed with veto-proof majorities, and Barack Obama thought it was politically necessary to nominally oppose same-sex marriage. And, yet, the Supreme Court justices they appointed provided four of the five votes necessary to not only strike DOMA down but hold that the right to same-sex marriage was guaranteed under the Constitution. Both Clinton and Obama applauded these decisions, and no serious contender for the Democratic nomination will ever again oppose same-sex marriage. A party's leaders tend to move with their parties.

To assume the Hillary Clinton of 1994 would be an accurate reflection of the Hillary Clinton of 2017 is to fundamentally misunderstand how politics works. When JFK made Lyndon Johnson his vice presidential nominee in 1960, labor and civil rights groups nearly revolted in view of Johnson's fairly conservative record representing Texas in Congress. When he became president, Johnson signed arguably the most progressive collection of legislation since Reconstruction. It wasn't that Johnson changed; it was that he was representing different constituencies in a different political context.

Needless to say, with Republican control of the House all but assured there will not be another Great Society if either Clinton or Sanders get elected. Indeed, the differences between a Clinton presidency and a Sanders presidency are probably much narrower than many supporters of either assume. But even if Sanders doesn't win, the support he's generating is having an effect. If the Democrats are going to keep moving away from their timid '90s, his supporters need to keep the pressure on.